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Why did the turbojet replace the piston engine?
Many people say that this was because aircraft powered by turbojet engines were faster during WWII. However the Grumman F7F-4N Tigercat, a fighter powered by a piston engine, flew at a maximum speed of 460mph and the Gloster E28/39 (first British jet engine aircraft) flew at a maximum speed of 466mph, which is not that great a difference.
Others say it's because aircraft powered by piston engines cannot fly as high as jet engine aircraft, but what is the reason for this?
Why did jet engine aircraft replace piston engine aircraft?

The German Me 262 jet fighter from World War II (first operational fighter powered by jet engines) had a top speed of 560mph, 100mph faster than the Tigercat.

You're saying that a "first" jet engine aircraft flew slightly faster than a presumably well-developed piston engine aircraft?

@immibis hardly first, the British, Russians and even Americans also had jet programs.  Germany was first to commit and enter serial production, and it had so many problems it was arguably not worth it, which may have been the Allies' reasoning.

@Harper a first. I'm going to assume they didn't have access to all the information from those other programs.

@immibis well then, you are correct, the first production jet fighter right out of the chute outflew the most evolved and refined piston airplanes.

The E28/39 was a small single-engine experimental design that was never expected to achieve particularly great performance: it was a testbed for the various engines it was fitted with at various times.  But it did surpass the (much larger and heavier) F7F-4N in ways other than speed: its operational ceiling was higher (it was flown to 42,000ft in a test flight, and it seems that other than a fuel shortage would have been able to go higher still) and with a larger engine fitted later on managed a speed 505mph.

Two more reasons the gas turbine supplanted the piston engine for aircraft use:
Power output. Aircraft piston engines have a practical limit on how much power they can put out, before becoming inefficient. This worked out to be around 3000hp. Two of the largest and most powerful piston aircraft engines that were also reliable enough for aircraft use are the Napier Sabre and P&W R4360, at around 3000hp, developed at the end of WW2. Yes, more power has been obtained from piston engines on land based vehicles, but they're either racing engines whose reliability is too low for aircraft use, or they're far too heavy for aircraft use, such as the 20k+ HP diesel engines that power cruise ships.
Gas turbines don't have those limits, one contributing factor being the lack of a reciprocating action. With a piston engine, each full stroke results in the piston accelerating to top speed, then coming to an abrupt halt and accelerating in the opposite direction... twice. Gas turbines that just spin can be made substantially larger while maintaining the reliability and efficiency that aircraft use demands.
Also, gas turbines tend to have a very high power to weight ratio, making them ideal for large aircraft use, where weight is very important.
Equating HP to thrust isn't simple as HP is raw power, while thrust includes altitude, velocity, and propeller/fan efficiency.
A simplified example was published on Aerospaceweb:

Luckily, we do have access to data from a NASA report that does
  provide all the data we need to illustrate a sample case. The data is
  provided for a Boeing 747-200 cruising at Mach 0.9 at 40,000 ft
  (12,190 m). In this example, the aircraft's engines produce 55,145 lb
  (245,295 N) of thrust, only a quarter of its rated static thrust, to
  cruise at a velocity of 871 ft/s (265 m/s). Using the equations
  provided above, we calculate the power generated by the 747 to be
  87,325 hp (65,100 kW).

Using that very simplified example, a GE90 producing 115,000 pounds of thrust would be putting out the equivalent of around 160,000 horsepower.
Also, the maintenance requirements on gas turbines are substantially lower, especially for the high output engines. For example, the very large RR Trent series turbofans have a TBO (Time Between Overhaul) of around 15,000 hours. On the large piston engines such as the R4360, the TBO was more like 1500 hours, and the very large piston engines, especially the radial engines, had a prodigious appetite for engine oil. Plus intermediate maintenance on piston engines that gas turbines don't need, like changing spark plugs, that had to be done frequently. The Convair B36, which had six R4360's, required 336 spark plugs. Not something you could do in your driveway in an hour.
Some of the gas turbine's reliability comes from it's lack of vibration. Large piston engines, with their reciprocating action, tend to vibrate a lot, which reduces the life of engine and auxiliary components, like fuel pumps and spark plug wires.
Thus, not only did the turbojet, turboshaft, and turbofan make possible aircraft that wouldn't be practical at all with piston engines, such as large airliners flying at 30k+ feet, they also lowered the cost of maintenance and the frequency of maintenance substantially.
There is one area where the piston engine for aircraft use is still the better solution, and that is when the engine gets small, below around 500hp. Gas turbines don't scale down all that well. The small ones are not fuel efficient, nor does the cost get substantially lower.
As an example of this, consider one of my pet daydreams - a single seat Mosquito helicopter. Aside from the ultralight version, two versions with larger engines (and requiring a FAA helicopter license) are made, the XE285, with an 85hp snowmobile engine, and the XET with a 90hp gas turbine engine derived from a backup power generator. The piston engine sells for maybe 2k USD and burns around 5gph, while the gas turbine sells for 10k and burns 8.5 gph.

Although I agree with your answer @tj100, I'd like to point out that during the time era of the op's question, propeller engines were much more reliable and the metal alloys at the time were best suited to fit the needs of radial and inline props (lasted longer and didn't warp under 400-600 degrees Celsius). As time went on, yes, turbines did outperform props in every way and unlike pistons, modern turbojets and turbofans have peak efficiency at their higher power outputs, not at lower thrust demands.

Both your points are valid but did not count when jets replaced piston engines. Only the massive development effort of the last 60 years improved the reliability of jets so much - the recommended use time for a Jumbo 004 was just 50 hours. After that it had to be replaced.

@PeterKämpf just a small mistype - you probably meant Jumo, not Jumbo :) Feel free to delete my comment afterwards!

@Antek You are right, autocorrect, and I did not catch it …

The process of replacing the piston engine with the turbine started slow, but accelerated rapidly. Initially, the pure turbojet gave speeds that propellers couldn't match. But, very quickly, the higher power output took over. The B36 had six R4360's and four J47's. The four J47's equalled the output of the six piston engines... although they were far more thirsty, used only for takeoff and sprints. By the late 50's and early 60's, the higher reliability and lower maintenance became evident. Finally, the high bypass turbofan put the piston engine out for good, as it also used less fuel.

Also, the Jumo isn't a good example. It's low reliability was due to the inability of Germany to get the metals to withstand the high temperatures. In contrast, the RR Welland in the Gloster Meteor lasted longer, as they did have access to chromium and molybdenum. Early reliability issues in the US P80 were related to the fuel pump for it's RR Goblin engine, not design problems with the turbine. It's important to make a distinction between unreliable for design reasons, and unreliable because the metals couldn't be obtained. The Jumo could have been reliable. Fortunately, it wasn't.

You know why the series version was the 004B? They had produced the "A" version before using chromium and molybdenum, but ran into vibration problems. The "B" version lowered the maximum speed to 8700 RPM, and that made a replacement using simpler materials possible. It was good enough. What happened 20 years later after the switch to jets is really not significant to why the switch happened 20 years before.

There are several benefits:

piston engines are best for driving propellers. At the same shaft horse power $P$, propeller thrust $T$ varies with the inverse of air speed $v$: ($T_{Prop} = \frac{P}{v}$). This means that the power requirement to keep a piston-powered aircraft flying will increase with the third power of airspeed at high speed. In order to fly 50 m/s faster, an aircraft with a top speed of 200 m/s will need an engine of almost twice the horsepower (195%, to be precise). A turbojet, on the other hand, has almost constant thrust over speed in the subsonic range, so $T_{jet} = const.$
Turbojets can make better use of precompression at higher speed. The kinetic energy of the airflow can be used to compress the air even ahead of the intake. At Mach 0.8 this yields 50% more air pressure relative to ambient air than in static conditions.
Especially important for military aviation: The early jets cost only a quarter of a high-performance piston engine to build in terms of man-hours. This offered a much better productivity in wartime where the available labor was a serious bottleneck. A single Jumo-004B needed only 375 hours to be built:

From Wikipedia:

Costing RM10,000 for materials, the Jumo 004 also proved somewhat cheaper than the competing BMW 003, which was RM12,000, and cheaper than the Junkers 213 piston engine, which was RM35,000. Moreover, the jets used lower-skill labor and needed only 375 hours to complete (including manufacture, assembly, and shipping), compared to 1,400 for the BMW 801.

The first point really is the most important, and it translates into much better altitude performance because the turbojet is in essence a big turbo-supercharger with a continuous combustion process at its center which produces thrust by ejecting air at high speed directly backwards rather than going through the complication of accelerating the air by rotating wings. This gave jet aircraft at high altitude (where the bombers and, consequently, the action was) both a speed and a climb advantage - they could break off combat at will, and their speed was so high that the bomber gun turrets could not follow them when they flew through a bomber formation. Jet-propelled reconnaissance aircraft could fly unharmed over enemy territory because no piston-powered aircraft could intercept them.
The Gloster E28/39 was only a demonstrator - if you want a realistic comparison, do it between the Grumman F7F and the Messerschmitt 262A, which could reach 560 MPH, 100 more than the F7F, and even topped 600 MPH in a special version with a low-drag canopy.
Regarding altitude: If you add enough turbo- and supercharging to the engine, a low-speed design can reach higher altitudes than most subsonic jets, but would be rather unpractical as a combat aircraft. In civilian use, a jet will reach higher cruise speeds which gives it an advantage over comparable propeller-driven aircraft. However, a piston engine remains the best choice for fuel efficiency.

One more point that I haven't seen mentioned yet: the fuel they burn.
Most piston engines burn gasoline, which requires a great deal of refinement. Aviation engines generally require gasoline with very high octane ratings (typically at least 100), which is still more expensive than the lower octane gasoline used in most automobiles and such. The requirement for high-quality crude oil was (for one example) why the war in North Africa was so important during the second world war.
Jet fuel, by contrast, is pretty much like kerosene or Diesel fuel. It does take some refinement to get from crude oil to jet fuel, but the process is simpler, and the quality of crude oil necessary isn't as high either. As a result, the higher volume of jet fuel burned is largely offset by the lower cost for a given volume, and the greater ease of obtaining crude oil of the required quality.
It is possible to power an aircraft with a Diesel engine. In the time frame in question (around the end of World War II) the only practical Diesel engines for aircraft were the Jumos. In some ways, a Diesel gives the best of both worlds--relatively low fuel consumption (even lower than gasoline engines as a rule) and the ability to use relatively low-grade fuel. There are, however, a couple of major disadvantages. The first is simple weight. A Diesel normally has a much higher compression ratio than a gasoline engine, so it has to be much stronger to withstand the higher pressures involved. The second is that some parts of Diesel engines (especially the fuel injectors) requires much more precise machining than virtually any part of a gasoline engine. This means a Diesel engine of a given capacity tends to be substantially more expensive than a gasoline engine of the same capacity.
So, for Diesels to make sense you need to use them for a relatively long-range aircraft--specifically, long enough range that the fuel savings outweigh (literally) the extra engine weight. Second, given the difficulty of manufacturing you probably want to restrict them to a relatively small number of aircraft. So, if you wanted a few long-range bombers (for example) they might well make sense. For fighters (short range, relatively expendable) they'd probably make a lot less sense.

Not all piston engines burn gasoline. Spark-ignited piston engines do, but compression-ignition engines (a.k.a Diesel engines) can burn kerosene too—and are the most efficient of the bunch, because they usually achieve the highest compression ratios. Their disadvantage is that they are heavier. However, with modern materials not as much, so they are becoming interesting for smaller aircraft.

@JanHudec: Yeah, I suppose I should add a note about Diesels.


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Why don't aircraft (commercial and military) use reflective visor windshields?
Just like those used on an astronaut's helmet, these reflective visors can help in better visibility when facing the sun (or any bright light source). But the windshields of most aircraft (commercial and military) look transparent from both sides. The whole point behind the question is to find out if it was experimented and if yes, why was it dropped?

Not solid answer but i guess it's about light being reflected in the cockpit at night.

And what about when these same planes fly at night, and the reflective coating makes the outside even darker than it already is?

I'm not sure about that. But, I guess the same principle used in an astronaut's reflective visor helmet can be used to overcome the situation at night.

At night, an astronaut just lifts the visor up. https://www.youtube.com/watch?v=Qg2KcAIFckM  The more important point though is to ask what problem would it solve? What makes you believe that there is a problem to be solved?

I think it might increase visibility for the pilots both inside and outside the cockpit (when directly facing a bright light source).

So does a good pair of sunglasses.

You should not formulate questions as "why don't we do something". This formulation assumes it has never been done, which must be wrong. Many stuff have already been experimented, not used, and then almost forgotten in aviation history (perhaps with good reasons).

That's right, but the whole point behind the question was to find out if it was experimented and if yes, why was it dropped?

If that is what you intended to ask, then you should edit your question to clarify.

Not a criticism but you aren't assuming the correct reasons astronauts have reflective helmets: The protection would be here to prevent over exposition to visible light. Actually gold or tungsten coatings are here to prevent exposition to cosmic particles, UV and IR. They also decrease exposition to visible light but not so much. So you are implicitly creating a new requirement for aircraft: Protection from cosmic particles, UV and IR which is arguable in the first place.

I'll assume you're referring to astronaut helmets only because of their sunglasses-like reflective properties against visual light, not other wavelengths.
There are some small efforts by manufacturers to add some reflective coatings to their windshields.  The 787 has a window coating by PPG that had a gold-based heating film that also reflected infrared light- useful because a cockpit can heat up quickly.  Military jets like the F-16 can have golden-tinted "Have Glass" cockpit windows but that's to reduce radar cross section, not to filter visual light.
There are several reasons visible-light reflective windshields are never seen.  The first is that optically it's very difficult to have reflection only go one way.  Reflective coatings work well for sunglasses and some car windows because the light coming in can be assumed to be much brighter than the light going out, so glare from inside is not a huge problem. In an aircraft, where that tiny light on the horizon could be a several-ton aircraft closing in fast, the requirements for night vision are a bit higher.   It should be noted that, for cars, reflective or tinted windshields are illegal in the USA for a number of reasons, including visibility.
The second reason is that bright outside light is a solved problem, so we don't have to resort to desperate measures like permanent reflective tinting.  Sunglasses use by pilots, even though not strictly necessary, is so widespread there's literally a style of sunglasses named "aviators" and the FAA has a safety brochure on selecting sunglasses (AM-400-05/1).  If the pilot doesn't like sunglasses, they can use sun visors and sun screens that may be part of the aircraft or provided by the airline.

Reflective materials cut down the amount of light let into the cockpit, which is useful in very bright sunlight, but would be undesirable at night. At night these materials could potentially blind the pilot, so you would have to make these materials retractable somehow, which would add complexity and weight. Over time these coating would be damaged by airborne debris, smashed bugs, and regular wear and tear. Add this that these coatings are expensive - outfitting them would be a significant cost.
Add to this that ever pilot would have different tinting needs - some people with less sensitive eyesight would need less tinting and others more. It's far cheaper and more effective for people to simply buy sunglasses.

How would that supposed to be working?
If you were normal glasses, you never ever thought about wearing sun glasses all the time, right? Because in so many situation, you do not need sun glasses.
As pointed out, even astronauts don't use it if they are not exposed to the sun (it's like a sun glass to them). So it's an obvious decision to let the pilots wear sunglasses.
The only thing that comes near to what you may think, are "sun visors"
These are adjustable and work like a big sun glass. They are however not overlayed with gold like no sun glass is. This is simply because there is no need for such a strong protection. We have the atmosphere that reduces the sunlight even further, the astronauts don't.

Go for a drive at night, with your headlights off and sunglasses on. Actually, don't. I don't want you to die.
Now imagine doing the same thing while landing a highly flammable tin-can with hundreds of lives counting on you, except this time the sunglasses are glued to your face.
You can see how this is a terrible idea for anything but daytime flight, right?

@Pondlife Windshields tend to be solid state systems, so tinting a window for daytime operation doesn't go away at night, or in overcast conditions.

(This answer pertains to military application)
A reflective windshield would increase the chances of the aircraft being seen. This is often NOT desirable in military application. The enemy being able to see that very shiny canopy reflecting light at them would increase the chance of being shot at.
Even a regular fighter jet's canopy reflections can be a detriment to the pilot. Dirty canopies reflect more light, and it is a crew chief's responsibility to keep that canopy clean, both to prevent the pilot from having issues seeing, and to prevent them from being seen. As a crew chief, I'd been blamed more than once for my pilot 'losing' in training missions because he was easily seen by others due to reflections off his canopy (I wasn't always too keen on polishing them.)

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Why is a 0 kt, vertical climb in a helicopter not safe near the ground?
In the "Test Pilot" column in the July 2017 issue of AOPA Pilot, one of the questions was

From reader David Franklin: If a given helicopter has a best rate-of-climb airspeed of 60 knots, its best angle-of-climb speed would be _____ knots.

The answer provided

Assuming a no-wind condition, zero knots of airspeed would result in a 90-degree climb angle. This would be neither safe (near the ground) nor efficient but certainly would be effective.

makes intuitive sense (climbing straight up gives the best angle, of course).
But why is it not safe near the ground? Does that change if there were wind (and no correction for the wind were applied)?
A suggested duplicate indicates reasons why going straight up is not as efficient, but does not mention the safety aspect at all.

I don't believe that this is a duplicate since the answers linked do not answer why it's not safe.

@Simon edited, but I don't see a way to remove the duplicate warning. Flagged for mod attention.

FWIW, I suggested this is a dupe because the accepted answer to the other question does include safety concerns as a reason not to take off directly: "will result in a rapid descent back to earth", "cannot produce lift or even worse, stall the blades". But as always, that's only my opinion and others may see it differently.

The mods will usually not intervene.  I've voted to re-open so it will go into  the review queue and everyone who reviews will see it. I doubt anyone will vote to keep it closed, but let's see. In the meantime, read this.

@Pondlife But my answer on that one only talks about power. You can have plenty of power but a vertical take-off is dangerous since you cannot safely autorotate if the engine quits.

@Simon That's a good point that I definitely didn't think about! I'll VTR too.

A vertical take-off, known as a "towering" or "confined area" take-off, is normally only used when it is not possible to take-off and remain in ground effect before gaining speed and climbing away.
For example, your operational need is to land in a clearing in a forest or perhaps a field surrounded by tall trees. In order to take off again, you need to  climb vertically until you've cleared the tops of the trees so that you can transition forward to gain speed.  You might need to use on at night (because you cannot see if there are any obstacles ahead) or when taking off from snow or sand when your vision will be obscured, making a vertical take-off safer.
It is technically defined as any take-off which requires you to climb vertically until out of ground effect.
In this answer, I've discussed the reasons why the power required to transition in ground effect to forward flight is much less than that required in a hover or a vertical climb out of ground effect.  Before attempting a towering take off, the pilot should conduct a power check to establish that they have enough power to hover OGE (out of ground effect).  If you do have enough power to hover OGE, then in theory, you could continue to climb vertically until the reduction in engine power output or lift (small effect) as you gain altitude reduces the power margin to the point where further climb is not possible without exceeding limits.
So, to the point of your question, why is it not safe?
The main reason is a scenario which is common to all helicopter operations, not just a towering take off.  Climbing vertically to 90 feet is exactly as dangerous as coming to a 90 foot hover in an arrival from forward flight.
This scenario is putting yourself into a shaded area of the height velocity diagram, known by pilots as the "avoid curve" or perhaps more accurately the   "dead man's" curve.  Importantly, this has nothing to do with how much power you have which of course, if the engine stops, suddenly becomes zero!

Source: Copters.com
In short, test pilots, using a fully loaded helicopter over level, prepared surfaces, try to enter auto-rotation from different combinations of height and speed.  At some point, they look at each other and say "a normal, well trained pilot, could only just auto-rotate safely from that combination of height and speed.  They plot these points on a graph, join the dots and say "see those shaded areas, don't go there".  It represents the areas where you will not have enough of the combination of potential and kinetic energy to make a safe landing.
As you can see, the towering take-off puts you deep inside the avoid curve.  This is the first safety concern.  If the engine stops, you will almost certainly crash.
I chose that curve, for an Enstrom F28, because it nicely illustrates that if you continued climbing vertically to 300 feet, you would pop out of the  top of the curve.  From this height, you could auto-rotate safely.
The second safety concern goes back to the power required. If you run out of power during the climb, the aircraft may start to descend into its own rotor vortex and can enter a vortex ring state.  In a confined area, you have no options for escaping it and certainly, all but the best pilots will not avoid a crash or, at best, a very heavy landing.  I'm a relatively low time private pilot and when I do my power checks, I want to see at least a 10% additional reserve over the measured power check.  There have been times when pilots have landed in confined areas but have then not had the power to hover OGE.  They have had to reduce the weight and/or wait for a lower temperature before trying again.
The third safety concern is the need for good skills and training.  When performing towering take-offs in typical sport and private helicopters, the pilot must be gentle on the controls. Relatively large or rapid control inputs cause large spikes in the power required. When you have plenty of speed, this doesn't really matter but when climbing vertically, you might be calling for more power than is available.  You must climb OGE slowly with gentle collective increases and, when clear of the top of the trees or other obstacle, ease the cyclic forward gently.  It is this last input which is especially risky.  If you push the cyclic forward as you would in a normal take off, you could find yourself running out of power and settling into the top of the tree with nothing left to give.  The safe way to do it is a slow climb but obviously, this leaves you in the shaded area for longer.  I was always relieved when I cleared the trees and got back into normal flight and the temptation, which must be resisted, is to increase your climb rate to reduce the time on the curve but of course, this reduces your power margins. The general principle is to use the power required and no more.  Gentle climb, gentle movements, be ready to pick up wind as you clear the obstacle, and you'd better have made sure before you get there that it's a head wind.
The fourth safety concern (and the last one to my knowledge) is not so immediately dangerous but can lead to trouble.  In a helicopter without a large power reserve, it is possible to reach a point where the power required exceeds the power available, especially if you catch a gust of wind. In this situation, the rotor RPMs will start to reduce or "droop". The only possible response is to lower the collective.  This normally means you have to give up and simply land and try again as above but any situation which leads to the rotor RPM dropping outside your control is to me, a safety concern.
All of this said, some pilots spend a lot of time operating in the shaded areas, for example in logging and power line check operations but they are appropriately trained, use machines chosen to reduce the risks, pay more insurance than the rest of us and accept the risk as "part of the job".

Jeez, this stack never fails at explaining how much more complicated helicopters are than a random gamer would expect o.o.

@StarWeaver No few of the fixed wing colleagues likewise don't understand the increased complexity.

@simon "Category A" helis are twins that can be safely operated under power after one engine fails, even in a hover. These types of departures are called "alpha departures."  https://www.law.cornell.edu/cfr/text/14/29.53

@rbp Do you think that's worth working in?

Do the charts make allowance for maneuvering to any landing spot within the glide range of the helicopter, or would additional height be needed if e.g. the contingency landing spot was to the rear?

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text:
What did seat belts look like in 1940s aircraft?
I first flew back in the 1940s as a four or five year old. I have a vague memory of a seat belt locked with a wooden peg inserted into a webbing loop. The aircraft was probably a Vickers Viking, a very unreliable aircraft.
We landed at Lyon, France, no wheels on the grass and we have a photograph of the crew and passengers in front of the downed aircraft in a field! Was there ever such a seat belt?

Welcome to Aviation.SE! Can you add that picture of the aircraft to the question?

In the 40s you would mostly have seen those lever clamp type buckles that were popular up to the 60s, at least in North America. They were replaced with the modern ones because they were almost impossible to release if you were hanging upside down in the belt.  What you recall was most likely a belt that was just a big leather strap with holes and a buckle, like an oversized pants belt, that was common on British a/c up through WW2.

Firstly yes I have a shot of the Aircraft on the ground in what looks like a field but is just off the Lyon airfield runway. It is a Vickers Viking operated by Airwork and the occasion was around 1948/9. I have not found a way to upload the picture. I cannot see the registration of the aircraft. Square windows! They don't do that anymore after The Comet. Happy to upload the picture if there is a way.

My sister has produced a date for the accident - May17th 1948 and the the flight was ex Khartoum to UK but no airport!

Extraordinary story! Btw, there is a book about Airwork, you may already know. I found a trace of a BEA report "aérodrome de Lyon-Bron (Rhône), Vicking (G-AIXS) 17 mai 1948", but it isn't available online, likely not digitalized. This was an Airwork aircraft and was lost 6 years later in an emergency return to Blackbushe. If I find something else I'll post it here.

Simply [edit] your question and drag the picture from your computer into the text edit box. The site will upload & host it for you.

@hutchinson is the problem with the picture that it's a paper photograph or a slide and you don't have a scanner to get the picture onto the computer?

I added in the pic with pax & crew from the deleted non-answer. Now, you just need to identify yourself! I'm guessing you're the young man standing closest to the squatting crewman.

Wonderful to see that photograph, I am the very small girl on the left of the group, standing in front of my parents....I remember this occasion fairly well, the cows scattering across the field as we came gently into the field...a few local taxis from the town came out to take us to a hotel...leaving the men to chamber aboard to see what the problem was, ( all engineers)

Your seatbelt, as a five year old, may have been an earlier version of the loops they still use for very young children when travelling on a passenger's lap.
However, the Vickers Viking was generally equipped with seatbelts. This undated picture of a Viking interior from the SDASM archives shows a buckled belt on the nearest seat.

source
The Viking first flew in 1945. This picture from 1946 shows a Viking seat being manufactured, clearly with a seatbelt, indicating they probably were fitted from the outset.

source

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What are the differences between the MiG-15 and MiG-17?
Apart from the extra wing fence and angled leading edge of the MiG-17, what are the differences visually between the two aircraft?

The leading edge is not just 'angled'; the sweep angle is 5-8° greater on MiG-17 (37° vs 45°), which is very noticeable. This was, in fact, the first and main modification of the airframe - in the chase for speed. The first MiG-17 prototype was even referred to as MiG-15bis 45°.

In addition to the elements on the wing mentioned by @Jamiec, on the rear, there are some little differences close to the rear air brakes.
See the picture below of a Mig-15:

The rear air brakes are in dark grey on this plane, the fuselage is smooth.
On a Mig-17, there is a small protruding part on the closed brakes; see this picture:

I cannot find if this change on the mechanics of rear air brakes is on all versions of Mig-17.

Your pictures also show what I've often considered the most obvious visual distinction:  the MiG-17 has a ventral vertical stabilizer, aft, under the jet nozzle.  I've never seen a MiG-15 with one (to my knowledge).

I'm surprised no-one's mentioned the length - the MiG-15 has a much stubbier appearance than the MiG-17, because it was rather shorter (10.10m vs 11.26m)
The wings of the MiG-17 are angled at 45°, rather more than the MiG-15 (helpful to identify from above), and the tailplane is has a small amount of extra rake too.
Overall, the MiG-17 has a longer, sleeker profile than its older cousin. Here's a comparison, 15 in blue, 17 in red.

The area of the ailerons appears slightly greater on the 17

Visually, the only differences are those you've mentioned - the extra wing fence and the angled vs straight leading edge.
The MiG-17, being developed much later was meant to be a far more advanced aircraft compared to the MiG-15. But visually, they were very similar indeed.

In addition to the greater angle of wing sweep and the additional wing fences, the wing of the MiG 17 had a different, thinner profile with a thickness/chord ratio of 1 to 10 or 10%, down from the MiG 15's 11%. This was still relatively much thicker than the 5% wing used on the supersonic McDonnell F4 Phantom. The superior efficiency of the MiG 17's wing at subsonic speeds, coupled with the lower wing loading made it more maneuverable than the F4 in the horizontal plane. The MiG 17 had increased power from a developed version of the Nene engine giving 7,450 lb thrust with afterburner. Early MiG 17s had the MiG 15's armament of one N37 37mm cannon with 40 rounds and two 23mm NR23 with 80 rounds each, but many later aircraft substituted a third NR23 for the 37mm gun, giving a combined rate of fire of around 2,500 RPM with ammunition increased to 100 RPG.

Depends on the version of MiG 17, surely? The MiG 17 PF had a completely different nose because of the Izumrud radar mounted on the intake splitter and the revised upper intake profile.
!


text:
What are the guidelines and regulations for building a helipad for multiple aircraft?
Are there any guidelines and regulations governing the ownership and construction of a multiple aircraft type helipad in
a) the USA
b) Europe?

Do you mean Helipads that are often seen on rooftops in cities? The ones I've noticed are only big enough for one craft at a time.  Or do you mean at a more remote location, like part of a pier, or an airport, where there is room for more than 1?

We already have multiple questions about building an airport in the US, e.g. here, here, and the basic answer is always the same: construction ultimately depends on local (state/county) zoning regulations. What exactly do you need to know that isn't already answered in those questions?

@CrossRoads I'm saying constructed both on  rooftops and those in remote locations, however by different aircraft trypes, I mean some have more weight than others and others have wheels instead of blades or rails as landing gear

@Pondlife I'd like to know the specific guidelines with regards to construction and approval of heliports like it has to be 5.this X 5.this diameter or wide, it has to have x to x to x concrete mixture advisory on non landing paved area at least 10.this x 10.this area.  It must have a 20.this x 20.this clear surrounding otherwise we won approve! If you let trees grow and continue to land you will flout the safety rules and go to jail, minimum x years to life...  measure ments in Scientific units like metres, centimeters and millimetres will be great appreaciated. Also Kgs and grams

The FAA publishes an Advisory Circular on heliport design.  It applies to heliports serving helicopters with a single rotor.  I don't believe that there are any regulations regarding "ownership".  They just have to be operated in compliance with appropriate FAA, state and local regulations (but these can get complicated)


text:
How is separation managed when there are only two parallel runways in a very busy airport?
In the world's busiest airports, how is separation managed between departures and arrivals when there are only two parallel runways like in London Heathrow. What is the minimum safe separation?

Shameless plug: Worlds busiest airports

With two runways, usually, one is dedicated to arrivals, and the other is dedicated to departures. That's the simplest way to handle separation -- only in-trail separation is involved.
That's usually the way traffic is managed at Heathrow (LHR) and Dubai (DXB), two of the world's busiest two-parallel-runway airports. At Heathrow, when in a westward flow (70% of the time) the runway functions are swapped about 3pm, to equalize noise impacts.
San Francisco (SFO) has two parallels, 28L and 28R, that are 750 ft apart -- very close. Under visual conditions, both runways are used for VISUAL approaches. Generally, aircraft arrive side-by-side, for wake avoidance.
For about an hour a day. 6am to 7am, when arrivals dominate, LHR allows arrivals on both runways. I don't know what separation rules are used. At SFO, under marginal conditions, both 28s are used for arrivals but aircraft are staggered and capacity is less than for visual operations.

Worth mentioning that SFO can, weather permitting, use the perpendicular runways (1L and 1R) for most departures, which permits more capacity than if they just had the two parallel runways.

The 'usual' (over 90% of the time) way that SFO is configured is: arrivals on Rwy 28L and 28R; departures on Rwy 1L and 1R. Both runway pairs are separated by 750 ft -- really close. If you look at https://www.fly.faa.gov/Information/west/zoa/sfo/sfo_aar.htm, you'll see there are several ways to manage arrivals: side-by-side, staggered, in-trail, etc., each with its own arrival rate.


text:
What is the wattage for strobes and anti-collision lights flashing lights on an aircraft?
Flashing anti-collision lights, also know as strobes on an aircraft can be seen on the aircraft  When flying at 36,000 ft during the day with clear skies.
What is their wattage (e.g 1000 watts) since they are so bright?

This question covers some of what you're asking. It would be very helpful if you would ask only one question at a time, that way we can point you to existing answers without dealing with the mess of "question A answers your point 1 and question B answers your point 2" etc.

Measuring strobe light intensity in watts doesn't make much sense. Watts are a measure of energy per unit time, and strobes are only "on" for a very short time. Second, for most lights, watts tells you more about the heat output than the light. For light output, you're probably looking for lumens.

Strobes are not measured in watts, pulse style high discharge lights are measured in Watt-Seconds due to the way they operate. Since the strobe is pulsed for a very short time the watt second gives you a measurement more or less equated to the brightness of a bulb of said wattage on for a one second. The FAA mandates the brightness of anticollision lights via their output in candles not watt-seconds or watts as those are somewhat better for comparing power draw than for comparing brightness of lights:

§ 23.1401 Anticollision light system.
...
(e)Light intensity. The minimum light intensities in any vertical
  plane, measured with the red filter (if used) and expressed in terms
  of “effective” intensities, must meet the requirements of paragraph
  (f) of this section. The following relation must be assumed:
$$ I_e = \frac{\int_{t_1}^{t_2} I(t)dt}{0.2 + (t_2 - t_1)} $$
where:

$I_e$ = effective intensity (candles).
$I(t)$ = instantaneous intensity as a function of time.
$t_2−t_1$ = flash time interval (seconds).

Normally, the maximum value of effective intensity is
  obtained when t2 and t1 are chosen so that the effective intensity is
  equal to the instantaneous intensity at t2 and t1.

With the use of LED's the units them selves draw less power than their older halogen gas style counterparts. For example this unit has a 36V 1A input which computes to 36 Watts of power for the strobe (remember P=IV) but clearly conforms to FAA brightness requirements. There are more options here that draw as low as 4 watts for continuous operation but again tells us nothing of the Watt-Second output of the unit. I can not find any units that list a watt/second equivalent for their output.

Very clear answer, thank you


text:
Does the person directing the plane to parking not risk getting ingested by a jet engine?
According to answers in this post, a jet engine can suck a human into its engines, even on idle power. Aircraft use their engines post landing taxi and into their parking space, and I notice people directing the plane to and from the parking space while engines are on.  Do they not risk getting ingested into the plane's engines?

A marshal should always ensure that he is in the line-of-sight of the pilot, failing to do so will effectively mean that the pilot is losing its extra sets of eyes. It is unable to see the hand gestures of the marshal guiding him into a parking spot.
To be visible for a modern jet liner pilot, you have to be meters in front of the nose of the aircraft. In the picture below, you have to be roughly on the right side of the orange line to be visible to the pilot. Modern airports use a digital marshal on a screen mounted to the terminal building.

Incidents of people getting sucked into the engine mostly happen due to miscommunication. Someone already walking up to the rear wheels with the blocks while the pilot spins up the engines to move the plane a little bit forward.

For a airliner there is no way to stay in sight of the pilot to guide them and be close enough to the engine to get sucked in. After the aircraft is parked the marshaller knows the danger zone for the engines and knows to stay away from them. In a lot of modern airports the marshaling is done by automatic systems and no external human is required to line the plane up.
There is a much bigger risk to the marchallers for the small GA propellor planes. There the spinning fan of death is right at chest height and if the pilot mishandles the controls could jerk the aircraft forward into the poor marshaller who only wanted to have all the planes on the apron in a neat row.


text:
How do conventional and T-tails differ?
What design considerations go into the decision between conventional tails and T-tails?  Functionally the horizontal stabilizer/stabilator are the same in both cases, providing negative lift, the elevator control and a method for pitch trim.  What are the differences though?
As far as I am aware the T-tails I have flown have T-tails for avoiding propwash (PA-44) or aft engine placement (EMB-145).  Are there other reasons for having a T-tail?  What are the aerodynamic consequences a pilot needs to be aware of with a T-tail (e.g. avoiding hard de-rotation on touchdown, issues at high AOA, etc)?

For gliders with T-tails the additional structural complications/weight are offset by less interference drag and more clearance for those special outlandings (think a barley field).

Though on most aircraft the horizontal stabilizer does indeed produce negative lift, for positive stability it is only required that the rear surface flies at lower angle of attack than the forward surface.

There is more to a T-tail than that:
Aerodynamics:

The placement on top of the vertical gives it more leverage,
especially with a swept tail.
Depending on wing location, it stays in undisturbed flow in a stall. Note: This is really depending on the details, the HFB-320 had a forward swept wing and a T-tail, which made a deep stall possible (and in one case fatal).
By designing the junction with the vertical well, the T-tail has less interference drag. It also helps to reduce wave drag, especially when using a well designed Küchemann body (the round, long, spiky thing on the tail junction of a Tu-154) by stretching the structure lengthwise.
It can help to increase the effectiveness of the vertical tail by keeping the air on both sides of it separated. At the other end, the fuselage does this already, so moving the horizontal tail up does not hurt so much there. As a consequence, the tail can be built lower.
Rear-mounted engines pretty much force a T-tail, but allow to keep the wings clean. Before CFD, mounting the engines on the wing created lots of problems, prompting the engineers to move to tail-mounted engines in their next design (DC-8 -> DC-9, B707 -> B727)

Structure:

The mass of the horizontal tail on a long lever arm (= the vertical tail) means that the torsional eigenfrequency of the fuselage will go down. This will be a problem in case of flutter.
As a consequence of the smaller vertical tail, a T-tail can be lighter. Note that the increased leverage means that the horizontal tail can be smaller as well. This reduces friction drag and is the main reason why most modern gliders have T-tails.
However, now the fuselage must become stiffer in order to avoid flutter. During flight test of the C-141 it was found that the antimetric wing bending mode would nicely couple with the torsional Eigenmode of the the tail, resulting in some scary footage. Also, a coupling between elevator rotation and horizontal tail torsion required to generously add mass balance to the tail.
Rear mounted engines also require more fuselage structure. The Boeing 737 was initially planned with rear-mounted engines, like the Sud-Aviation Caravelle, which it was meant to replace. By selecting the final version with wing-mounted engines in the underslung design, Boeing could reduce the empty weight of the 733-100 by 700 pounds.

Control:
A T-tail produces a strong nose-down pitching moment in sideslip.
If it were not for the flutter and pitch-down, T-tails would be more widespread ...

uhmmm very interesting but now I can't understand why commercial airliner strictly prefer conventional tail instead of T-Tail. With all these advantages, why at least some of commercials does not consider this solution? (apart some minor commercial airplanes, I saw it above all in military ones like C5 and C-17)

@LucaDetomi: Airliners with their sweptback wings run the risk of deep stall if the tail is too high. Also, the flutter speed and required stiffness is a real problem and should not be taken lightly. After the Felthorpe Trident crash, Tupolev increased the tail on the Tu-134 by 30%, just to be safe from deep stall. This kind of modification makes a T-tail less attractive than a conventional tail.

There's a lot to this, and I'm no aircraft engineer, so if there are any other answers, I'll happily delete this. Anyway, from what I've been told:
The T-tail sticks the elevators out of the disturbed air of the wings, prop, and (usually most of) the fuselage which gives you better elevator authority, and makes a tail stall less likely.
It has some drawbacks though, by putting the elevators directly in the (turbulent) separated flow from the wings during a stall can put you in a (more or less) unrecoverable deep stall.

(Picture from the linked Wikipedia article)

For the most part this is correct, although if airflow is disrupted over the tail the nose should actually come down because the horizontal stabilizer is what holds the nose up in the first place. I suppose depending on the aircraft and the weight and balance situation though maybe it is possible.

@p1l0t; you are correct; I was however under the impression that the condition is more or less stable, pushing the tail back into the vortex when it tries to leave (such as when the nose tips over due lack of rear downward pressure). I can't really say I know the aerodynamics of it though, so I might be very mistaken.

I suppose it is possible to disrupt the flow enough to where the controls are ineffective but not enough that it can still hold the nose pitched up to a stall although it seems like long shot and/or a poor design. Most of the (small aircraft) T-tails I have flown it takes a bit of extra effort to stall the aircraft hard because gently the disruption just lets the nose back down and then you aren't stalled anymore.

in large a/c deep stalls can get quite stable because of fuselage lift and (especially in case of airliners) sweptback wings that move center of pressure forward when stalling. For smaller aircraft though it is very difficult to hold nose high enough to overshadow a T-tail

@Radu094: You might want to watch the ACI/Mayday episode of BEA Flight 548 in which a T-tail mounted Hawker Siddley Trident entered an unrecoverable stall: http://en.wikipedia.org/wiki/British_European_Airways_Flight_548

@falstro - You are not mistaken. The basic danger of a T-tail in a stall is that because the tail is out in undisturbed airflow, there's little tactile warning the aircraft is about to stall (normally airflow from the wings begins to buffet the elevators). The primary indication is a loss of lift, which the pilot would naturally correct by pulling up, deepening the stall.   Once in the stall, the tail is sheltered as your answer shows. A further problem is the swept wings, causing the wingtip to stall first, moving the center of lift forward and keeping the nose high.

To combat these tendencies, stick shakers give the pilot the tactile feedback similar to what he'd get in a conventional tail, while stick pushers will push the column forward in a pre-stall AOA, countering the pilot's natural tendency to try to nose up. Even then, the risks inherent in flying a large T-tail are too great for U.S. airlines; the 727 is pretty much gone, the MD-80 is retiring, and the remaining T-tails still in production are smaller narrow-body regional airliners with more docile characteristics (and fewer lives at risk).

@p1l0t: It should be, yes, but if the aircraft's COM is too far back for some reason...

The considerations in the roe's answer are entirely correct but there might be other factors to take into account.
First, it is true that using conventional tail leads to the fact that the airflow over the tail might be disturbed by the main wing and/or the engines and/or the fuselage. However, the downwash induced by the main wing on the flow is taken into account (for the cruise conditions) in the design of the tail in order to reduce some negative aspects of the interaction between the main wing and the tail.
Another major difference between these two configurations concerns the stability. As I already explained in this answer, the tail is used to create some lift that is required to fulfil the trim relations. Regarding the "vertical" force equilibrium equation, there is no real difference between the two configurations but there is a big one for the moment equilibrium.
Assuming that you have the same amount of lift generated by the both configurations (this is relevant due to the "vertical" force equilibrium), a quick sketch will convince you that both the angle and the lever arm are different. The conclusion of this study cannot be drawn without a specific example but I hope it is clear for you that stability is really impacted by the choice of the tail.
From a structural point of view, when flying transonic (or even supersonic) it is not good to have a T-tail configuration because it usually induces flutter on the tail.
Finally, at a lower level but still a difference, using a T-tail increases the wake (compared to a conventional configuration, where the tail is almost in the wake of the main wings and the fuselage) behind your aircraft and thus the drag you need to overcome is larger.

I am not so sure about your argument for added drag...

@yankeekilo But you do agree that the wake is wider?

hmmm... "wake size" is quite undefined. The resulting drag is what counts. A stabilizer in undisturbed airflow will produce better L/D than in turbulent flow, as well. So unless you have some sources for that argument, I would not buy into it.

A T-tail has structural and aerodynamic design consequences. The structural considerations are of course the increased weight of the vertical tail due to now having to support the forces and moments on the horizontal tail, including strengthening for flutter. The vertical tail can be shorter due to the end plate effect of the horizontal tail, and the moment arm to the CoG is longer - however for most higher subsonic speed aircraft these effects merely reduce the weight penalty.
The T-tail stays out of ground effect for longer than the main wing. Upon approaching the ground, the increase in wing lift causes an auto-flare: the aircraft lands itself. From the wikipedia page of the Handley Page Victor:

One unusual flight characteristic of the early Victor was its self-landing capability; once lined up with the runway, the aircraft would naturally flare as the wing entered into ground effect while the tail continued to sink, giving a cushioned landing without any command or intervention by the pilot.

The aerodynamic consequences of a T-tail have most to do with stability and control in stall and post-stall behaviour, and can be grave. The Fokker 28 and F100 had stick pushers that acted upon detecting a high angle of attack, making it pretty much impossible to keep the columns at aft position. The reason for this is the reversal of the $C_M$ - $\alpha$ slope of T-tails, as depicted below.

Graph A is for a tail height of 2 * MAC
Graph B for 1 * MAC
Graph C for same height as MAC

The aeroplane is aerodynamically stable when the $C_M$ - $\alpha$ slope is negative, such as in cases B and C. For configuration A, the slope becomes positive after the stall point, meaning that the nose wants to increase upwards after reaching the stall - not a good situation.
The stall speed must be demonstrated during certification, and safe recovery from a stall is a requirement. A stick pusher prevents the aeroplane from entering the deep stall area.


text:
Why was the Boeing 377 "Stratocruiser" frequently landed nosewheel first on touchdown?
Why was the Boeing 377 "Stratocruiser" frequently landed nosewheel first on touchdown? In the mid-1950's I had often observed Northwest Airlines' B377's frequently being landed that way at the old Minneapolis-St. Paul airport.
A family friend and PanAm First Officer who frequently flew the SFO-HNL run in B377's told me that (as best as I can recall now) the reason for landing the B377 in that configuration had something to do with help in "setting or unlocking the nosewheel steering" for directional use when the aircraft was fully down on the ground.
As the B377 was Boeing's prototype for the "Stratocruiser", I've wondered if their wartime B-29 "SuperFortress" also was, or could be, regularly landed nosewheel first as well?
And then, during WWII, were there any other tricycle geared two- and four-engined "heavies" that were also meant to be, or could be, landed nosewheel first?

Here is a video of a Boeing 377-SG (Super Guppy) landing which shows no flare and touching down nose wheel first.

@RonBeyer -- that's actually a very interesting video -- it looks like the A/C touched down very slightly nose high (mains first) then bounced and landed practically in a 3 point stance on its 2nd touchdown.

This 377 video and this 377-SG video both appear to show actual nose wheel touchdowns. Also of note, a Caribou nose wheel touch and go.

The Caribou nose wheel touch and go was an airshow stunt and really has no relevance to the question.

The closest anyone came to answering this question correctly was the reference to the inboard wing spoilers mandated by the CAA (one of the reasons the aircraft's entry into service was delayed for a year).  Now that we actually have a C-97 flying again in 2017/2018 we will be able to see why this procedure is used.
A lightly loaded Strat can be landed on the mains but not much before the nose touches. The recent flights of 'Angel of Deliverance' were flown very light, around 89,000 lbs so landings were not much different than in a B-29, but add payload and those spoilers and longer fuselage change everything.
Also, the spoilers were never removed on any of the commercial 377 as was mentioned before. They were mandated for the civilian operators right to the end of their service lives, including on the modified Super-Strats that PAA flew. They deployed whenever flaps were lowered 10 degrees or more, and the purpose was to deflect the airflow over the inboard portion of the wing where it met the fuselage where, unlike other aircraft types, Boeing had not added a fairing. Without the fairing any sudden changes in wing angle would disrupt airflow over the inboard wing causing a stall. Early pilots (including the CAA) quickly learned that if they attempted to flare the aircraft as they would in a Douglas or a Connie the 377 would drop like a rock onto the runway. Not exactly the thing to do with tired First Class passengers after a 9-hour flight. This behavior even occurred in flight at higher air speeds with sudden pitch inputs, and it was this problem that prompted the CAA to demand the modification.
Several solutions were attempted for the nose pitch issue including a technique developed by the Air Force where anything other than a lightly-loaded C-97 would be tipped slightly to one side (usually the upwind side) and alighted on one main and the nose. This was possible because of the 3 degree angle difference between the nose wheel and the mains. If one watched old footage of the Strat or 97 you can see this technique (look for the 1951 film 'Star Lift' starring Doris Day. Rotten movie, but fantastic Stratofreighter footage!)
The problem with the dip-a-toe technique was that the airplane would then hop around on the various gear until lift was lost, less than satisfying on a cargo hop but on a commercial flight a serious source for complaints.
It was United Airlines' pilots that found a better solution with their Mainliners. They elected to carry an additional 5 M.P.H (later knots) into the landing, roll on with the nose wheel while still supported by the wing and wait for the back end to gently settle; finally a smooth solution to the flat landing attitude. United released a color promotional film in 1950 about flying to Hawaii where the technique was clearly demonstrated (and United's CEO 'Pat' Patterson nor its senior flight managers would ever have approved a film for national theatrical release with a "bad landing"). The landing, which is supposed to be at Honolulu but is actually on Runway 28R in SFO, shows the 377 gently touch on the nose and then roll right off camera--still floating on the nose. A video taken in the 80's of a cargo C-97 in Anchorage shows it touch on the nose and the pilot deliberately hold it there with a punch of smokey power before the mains come down. Look for both on YouTube.
These days this technique is often seen with NASA's Super Guppy, which has a further elongated fuselage (and everything else!) Despite having the original nose gear replaced by a shorter but tougher 707 gear the Super Guppy must rotate and land at higher speeds and often spends several seconds rolling on the nose.

Apparently, the nose first landing was necessitated by the aircraft's tendency to enter into a stall if the nose was brought up too far up. According to one of its pilots:

No amount of heaving back on the pole would induce the mainwheels to make contact first. Various explanations were offered for this peculiarity... Others pinned the blame on the pernicious lift-spoilers.
Why build a splendid wing and then fit lift spoilers? The story was that the Civil Aeronautics Administration (CAA: the FAA-to-be) would not give the type its Certificate of Airworthiness because a wing was apt to drop when the aircraft stalled. The CAA wanted the nose to drop first, and the only swift remedy was to destroy an area of lift near the fuselage.

A similar discussion can be found here. However, this seems to have changed later. From the same article:

Ironically, after BOAC had operated the type for about nine years it was decided that lift-spoilers were not necessary, and they were removed. I was then flying later types, but those who were still on Strats told me that it was then a much better-behaved aircraft.

Another thing that supports this theory is that the military version, the C-97 Stratofreighter seems to have landed normally, according to its pilot:

The control wheel is eased back at 90 mph to clear the nose wheel from the runway. The airplane will fly itself off at 100 to 120 mph depending on the load.

and

Normally the nose wheel is kept off the ground for the first thousand feet, but it can be dropped immediately for cross-wind landings.

So, this seems unique to the Stratocruiser (and its derivative, the Super Guppy). B-29s as far as I know, landed main wheels first.

You are indeed correct that both the B-29 and the C-97 landed in a quite flat attitude.  Randy Sohn mentions this in a report on flying FiFi for the first time:

Normal landings can be made with either 80% or full flaps. The aircraft has more of a tendency to land nosewheel first with full flaps and in fact, the first landing at Harlingen occurred this way. We used to do our short field landings this way with the C-97s, touching down precisely where we desired, although the USAF certainly viewed it with a jaundiced eye. With 25° of flaps as normally used in a crosswind it's fairly easy to strike the tailskid bumper. Any scrape marks on this heavy iron forging requires a round of beer for the crew!

Simple fact. Tricycle gear aircraft were never designed to be landed on the nose wheel. That fact that it was routinely done on the B-29, C-97, B377, etc. does not change this fact. At most it says it was a difficult aircraft to land CORRECTLY.
I maintain that anytime you see an aircraft land nose wheel first, it is a bad landing and nothing more.
War Department Training Film: How to Fly the Boeing B-29 Superfortress: B-29 Flight Procedure & Combat Crew Functioning

When you touch the ground the plane should be slightly tail low,. and going  and going between 95 and 100 miles per hour. Notice how the main wheels bear most of the shock of Landing. Then the ship slowly settles forward. Don't apply brakes immediately, let the plane lose some of its speed rolling.
More info: Why do planes always land on rear wheels instead of the nose wheels?
Aircraft land on the main wheels. For aircraft with nose wheel it is the back ones, but for aircraft with tail wheel (also called “tail-draggers”) it is the front ones. In either case the main wheels are very close to centre of gravity and carry most of the aircraft's weight, the nose or tail wheel only carries a small fraction of it.
The aircraft must land on wheels that are close to the centre of gravity (longitudinally). If they were not, the force on the wheels would create a moment that would violently pitch the aircraft. Actually, tail-draggers tend to bounce on landing a bit because there still is some moment left and in case of tail-draggers it pitches the aircraft up
Also:  https://www.quora.com/Why-is-an-airplane-nose-up-while-landing
Even if you don't drive the nose gear up into the aircraft, you can still have a bad day if you touch down nose gear-first -- you might wind up "wheelbarrowing" (rolling along on your nose gear, which will caster (pivot) VERY freely and could offer you a breathtaking view of the grass next to the runway).  Then again, you could emulate an aquatic mammal and "porpoise" (push down the nose gear, let it spring you backwards to bounce off the mains, which will bounce you back onto the nose gear, et cetera ad nauseum) until you (a) get sick; (b) strike the ground with the propellor; (c) collapse the nose gear, or (d) all of the above.

My question was "Why?" the B377's I saw often touched down on the nose wheel first and then rotated onto the main gear to complete their touchdown and landing.  Main gear first followed by the nose gear may have been the standard landing configuration, but nose wheel first was obviously not prohibited.  One possible reason for what I saw while I was stationed at NAS Minneapolis -- a slight rise with residential housing was not very far from the end of the runway where I was watching.  So the approach angle on final for those NWA B377's may have been necessarily steeper than ordinarily done.

My answer is that the landings you saw were simply bad landings.

Bad landings? Well, you know the story about "a good landing is..." ;-)

This answer does not authoritatively address the Boeing 337 procedures in question.

authors: К. Келлогг Смиф


text:
Do commercial airliners use supercritical airfoils?
I was looking how speed is distributed on this B747 airfoil:

Source.
Nearly all of the upper surface has air flowing above Mach 1. I'm wondering if this is frequent for commercial airliners to use supercritical airfoils? I'm particularly interested in the A330 case.

those are 2/3 different questions, which one do you want answered? What's the point of the image?

Supercritical aerofoils are definitely widespread in modern airliners, including the A330. In fact, the A300 which is the predecessor to the A330 was one of the first airliners to fly with a supercritical wing.
The reason for this is that maintaining slightly supersonic flow over the majority of the upper surface keeps it at high speed, hence producing low pressure and lift for longer and it also shrinks the shock from flow decelerating back to subsonic, compared to a conventional foil. As well as these direct aerodynamic benefits their thicker t/c ratio compared to efficient conventional sections makes the wing structure easier to design, making them a no-brainer for pretty much all modern airliners.

Can you expand t/c ratio for dummies? Thickness to chord?

That's exactly it. Having a thicker wing means the spar(s) can be bigger in the vertical direction, so it is easier for them to resist bending.

The wing is swept 37.5°. That means shock wave only forms when the stream exceeds M1.26 (1/cos 37.5°) and that only happens in the last quarter-or-so chord.


text:
What was 'Lufthansa Express'?
I found this picture earlier with a Lufthansa express livery:

It also appears to have been on a few larger aircraft like the A300:

Could somebody enlighten me as to what this operation was or the difference to mainline Lufthansa? I tried to search but couldn't find anything.

I found this forum discussion from a few years ago, which stated:

LH Express was their brand name for domestic services for some years in the mid 90s. I'm not sure when the LH Express name disappeared, but they definitely were not promoting the Express name in 1997 any more. So the aircraft you saw was probably just not repainted yet. LH used to operate B737 of various series and several Airbuses.

One of the guys went on to say it was a low-cost domestic route, set up in competition to Deutsche BA. Unfortunately, it did not succeed enough in competition and was eventually shut down. They did fly some small Boeings like the 737, and the Airbus 300 and 310.
Additionally, a NY Times article from 1992 gives a small blurb about the startup of the line:

Under the new strategy, eight key domestic German routes are to be served by a special spin-off division, Lufthansa Express, that promises passengers a better on-time record, faster check-in and a chance at bargain prices.
...
Another innovation of Lufthansa Express will be bargain prices on late-night and short-notice flights. Passengers get a 55 percent discount savings on flights after 7:30 P.M., even without advance reservation, for example.
...
The most controversial aspect of Lufthansa Express is something passengers are unlikely to hear much about: The starting pay for a crew on Express flights will be about 25 percent less than on traditional Lufthansa flights.

Another thread here has a few minor other details. Interestingly enough, Amazon still has a listing for a model LH Express 737 (out of stock).

There is always a B-scale wage hiding behind rebranding like that.

@casey i think i found the pic originally in a forum talking about the germanwings operation they're expanding...

@casey the lower ticket price has to come from somewhere, and with maintenance and fuel costing the same, it can only come from service and/or crew pay, with crew pay being the main factor in determining cost as service even at the time was already minimal on inter-European and especially European domestic routes.

@jwenting That is a common rationalization, but that is all it is.  The main factor in determining cost is an airlines ability to manage fuel costs.  When they can't do that, they come to the crew but in reality the cost of the crew is far outweighed by fuel and the potential savings for the airline by reducing crew pay quickly diminish as fuel costs increase.

@casey for an airline like DLH, the fuel cost per passengermile would be identical for their domestic and foreign operations (given the same aircraft type), so in order to lower cost within the existing framework the only option is to lower crew cost. They no doubt also try at every turn to reduce fuel cost, and ordering as a single operator for all their bases would help achieve that, giving them an edge there and then over smaller competitors.

@jwenting "the only option is to lower crew cost"... or they could price their product according to its costs.  If fuel prices go up, ticket prices should go up, not crew pay come down.

@casey and price it too high to sell tickets... If your competitor lowers prices by lowering staffing cost, there's little you can do but either do the same or go out of business. Your misguided idea that you can just charge whatever is needed to meet the next 154% pay increase demanded by the unions is false.

@jwenting you have an absurd view if what goes on in labor negotiations. Perhaps it is different in Europe but in the US we fight just to keep wages in pace with inflation. Our bargaining agreements also never expire and negotiations to amend can take years. Self help is not a real option. We can continue this in chat if you want.


text:
What restrictions are there for flying near urban areas in the United States?
Say you've got your own plane and take off and land from the same airport.
Weather is good, fuel is good, etc...
What would be the restrictions for flying near urban places like a city in the United States?
I live near a bunch of sea-planes that take off and land from lakes encircled by high-rises. Never thought about it till now, but how is that and other private flying entities like news choppers and ad-banner planes governed?

This varies from country to country but here in the US the Federal Aviation Regulations define the minimum safe altitudes:

Sec. 91.119 Minimum safe altitudes: General.
Except when necessary for takeoff or landing, no person may operate an
  aircraft below the following altitudes:
(a) Anywhere. An altitude
  allowing, if a power unit fails, an emergency landing without undue
  hazard to persons or property on the surface.
(b) Over congested
  areas. Over any congested area of a city, town, or settlement, or over
  any open air assembly of persons, an altitude of 1,000 feet above the
  highest obstacle within a horizontal radius of 2,000 feet of the
  aircraft.
(c) Over other than congested areas. An altitude of 500 feet
  above the surface, except over open water or sparsely populated areas.
  In those cases, the aircraft may not be operated closer than 500 feet
  to any person, vessel, vehicle, or structure.
(d) Helicopters,
  powered parachutes, and weight-shift-control aircraft. If the
  operation is conducted without hazard to persons or property on the
  surface--
    (1) A helicopter may be operated at less than the minimums
  prescribed in paragraph (b) or (c) of this section, provided each
  person operating the helicopter complies with any routes or altitudes
  specifically prescribed for helicopters by the FAA; and
    (2) A powered parachute or weight-shift-control aircraft may be operated at less than the minimums prescribed in paragraph (c) of this section.

In your case, the sea-planes can fly closer than regulated since it falls under the "Except when necessary for takeoff and landing" clause.
These minimums apply in all air spaces however different airspaces surrounding cities (typically Class B and Class C) may prevent you from ever getting within 1000ft (or even a few miles) of the city due to clearance. For example you can't get near a city under a bravo space without ATC clearance and even then you can't fly where you want like in other airspaces.

but how is that and other private flying entities like news choppers

News choppers and the like still must fly by these rules. They often compensate with bigger camera lenses. The somewhat exception to this rule is generally police, fire, and rescue/medical operation choppers/aircraft. This of course is taken on a case by case basis but ATC usually gives them precedent and clears them for whatever they ask within reason. I actually met a guy that was on the council that designed the Philadelphia Bravo Airspace. The airspace is specially designed so that the medical helicopters can take off and fly under the bravo shelf from any hospital in the city. They can do this and still be a safe distance from buildings as well.

and ad-banner planes governed?

Banner towing planes, like helicopters must also fly by these rules. Although they are not seen in cities all too often I generally see them at the beach. Although beaches are generally not defined as a congested area and generally the planes are flying over "open water" thus they must be only 500ft from the people on the beach (depending on how you interpret the law).

In the USA there is also the ubiquitous FAR 91.13 No person may operate an aircraft [....] in a careless or reckless manner so as to endanger the life or property of another which may come into play under certain circumstances.

I think it would improve the answer if you also included information about the various air spaces.

I have no idea what (a) is trying to say, but in layman's terms: 1000 ft for cities, and 500ft everywhere else? Regarding the other stuff, does that mean it's legal to paraglide in cities O_O?

@House3272 I tackled part (a) over here. For paragliders I imagine they would fall under FAR Part 103 (ultralight vehicles, they just happen to be unpowered), so they're prohibited from operating over congested areas, like cities.

Ahaha that sounds about right, thanks!

@OSUZorba How does airspace impact the minimum altitude?

Section (d) (1) Where is that information found?

@stevekuo the question asks about restrictions flying near cities, the word altitude never appears in the question. Airspace, especially class B airspace,  creates a lot of restrictions around many urban areas.

The FAA does offer waivers for lower operations that are for the purpose of protecting public interests. Generally, waivers can be obtained allowing operations as low as 500 ft from the surface over congested areas.


text:
How well can a helicopter handle someone jumping onto it while taking off?
I see it a lot in movies, curious how say...an Robinson R44 would respond to a 200-pound man jumping and grabbing onto the skids while it's ~10ft off the ground and in the process of taking off??
Edit:
more specifically, how dramatic would the effect be?
with Hollywood physics, the chopper would stumble as if the hand of god lightly slapped its side?

Well, if it was in a hover, then lift=weight and any addition of weight would cause a descent. In the case of taking off, lift>weight, so as long as that ratio remains true, the helicopter will continue to take-off (or hover). It works in the opposite way when somebody jumps out of a helicopter, which happens in the real world quite often.

Oh sorry, I should have clarified more. I meant to ask just how dramatic the effect would be. In hollywood physics, the heli's would dramatically stumbles as if the hand of god lightly slapped one side of it.

@House3272 You should include that in the question so people can see without reading the comments.

There's some pretty dramatic footage of a news helicopter that helped rescue people from the Potomac after the crash of Air Florida flight 90. They picked people up with ropes and dragged them onto the skids. The pilot was expecting it, but it didn't seem to budge at all. And it's not a helicopter designed for rescue

The total mass of a light helicopter is about 1000 kg (depending on type and actual payload, of course). The 200 pound guy adds about 10%  to the total mass (and weight). The skids are relatively close to the centre of gravity (COG).
Immediate impact

Kinetic energy

In terms of mechanics, the jumping man will have a mostly inelastic collision with the helicopter, and he will transfer both, kinetic energy and impulse accordingly. One may simply choose the helicopter as reference coordinate system to calculate the resulting change of (vertical) speed for the helicopter:
$$\Delta v_\rm{H} = \frac{m_\rm{G} \Delta v_\rm{G}}{m_\rm{H}+m_\rm{G}} = \frac{1}{11} \Delta v_\rm{G}  \ \ \ \ \ \ (m_\rm{H}=1000 \rm{\,kg},\ m_\rm{G}=100 \rm{\,kg})$$
In the movie, the jumping man will just make it. The relative speed will be close to zero, and divided by 11 will be even closer to zero. If he had a significant speed relative to the skid, he would not be able to hold himself.
The transfer of kinetic energy is negligible for the stability of the helicopter.

Added weight

The total weight of the aircraft increases by 10%. This sudden change creates a jolt which is clearly perceptible inside the helicopter, also suddenly changing the vertical acceleration. The (vertical) speed is the mathematical integral of the (vertical) acceleration. The speed will steadily change. The same holds true for the (vertical) position of the aircraft, which is the mathematical integral of the (vertical) speed.
In other words, the inertia of the bigger mass will prevent sudden  change of vertical speed. For the pilot, this 10% disturbance will be very obvious, and he needs to counteract.
(Note that there was a related question recently: What would happen if a plane lost half of its weight instantly?)

Imbalance

The imbalance caused by the guy hanging somewhere else than under the COG creates a torque. This torque creates an angular acceleration. This angular acceleration integrates to angular speed, which integrates to roll and pitch respectively. While the angular acceleration starts suddenly, the angular speed can only change steadily.
The helicopter will not loose its attitude in a fraction of a second, like it happens in Hollywood movies.
Countermeasure
The pilot will use the Collective control to counter the added weight, and the Cyclic control to counter roll and pitch. Provided that the pilot reacts timely enough, it should be possible to stabilize the helicopter. 100 kg additional mass should not prevent the helicopter from climbing, unless it was already overloaded and without safety margins before the 200 pound guy arrived.
More critical is the torque created by the offset load and the resulting COG shift. I am not aware of the roll and pitch performance of small helicopters, but I believe that they are able to fly with somebody standing or hanging on a skid. Asymmetric load of this magnitude will likely impact stability and manoeuvrability, but will not necessarily cause a crash.
If the fearless 200 pound guy instead would jump and hold to the tail skid, the additional weight would be much further from the COG, and the outcome probably be disastrous.
Safety
This does not mean that it is safe to continue the flight with the 200 pound guy hanging anywhere on one skid. Pilots always need to verify if the amount and distribution of the load is within the performance limits of their aircraft. See "Helicopter - Weight & Balance, Performance" for some explanation and example (note Figures 2-5, 2-6, and 2-7). Depending on the helicopter performance and the load distribution before the guy jumps, the new distribution may be within the specified safe longitudinal and lateral COG envelopes, or not.

I assume all super-villain helicopters come with a manufacturer COG table for mass with Hollywood leads hanging from a skid, for easy reference? :-)

@DanSheppard Indexed by hair color, because I'm pretty sure I haven't seen a superhero or a supervillain wearing a hard hat while pulling that stunt.

$200\,\mathrm{lb}$ is about $90\,\mathrm{kg}$. As long as the helicopter was generating a lift force at least $90\times 9.81 \approx 880\,\mathrm{N}$ in excess of its weight, then that lift force is enough to continue to accelerate plus helicopter upwards. Wikipedia says that the loaded weight of an R44 is about $1\,134\,\mathrm{kg}$ ($2\,500\,\mathrm{lb}$) so a force of $880\,\mathrm{N}$ would be accelerating the helicopter alone at about $0.78\,\mathrm{ms}^{-2}$ ($2.5\,\mathrm{ft\,s}^{-2}$). So, as long as the helicopter was already accelerating at least that fast, it will continue to accelerate upwards.
I'll let other people deal with the effects of the unbalanced load.


text:
Would one expect Canadair CL-215 or CL-415 planes to be equipped with a working ADS-B transpoder?
In a forrest fire in Greece, on which according to news sources eight such planes are operating as firefighters, no planes can be seen on Flightradar24.  Only a fire service's helicopter can be seen flying around.
Note that the planes in question are operated by the Hellenic Air Force.

Military operators can request that their aircraft are not shown on flightradar24.

Operators of private or sensitive aircraft may request their tracking details be restricted or not displayed. Generally, aircraft requesting that they not be displayed on Flightradar24 are military aircraft.

From: https://www.flightradar24.com/blog/whats-this-plane-doing-answering-recent-frequently-asked-questions/
Whether or not an airplane is equipped with ADS-B is entirely up to the operator. Both the CL-215 and CL-415 were designed before ADS-B existed. However, if the mission demands it, ADS-B capabilities may be retrofitted to existing aircraft. Whether this is the case for these particular Canadairs, I do not know (I expect not), but regardless, it's impossible to make any definite conclusions based on the absence on FR24 and related tracking websites.

I don't know if Greece requires ADS-B, but even if there was such a requirement, it's unsurprising that you wouldn't be able to see military aircraft on FR24. Operators, private or public, can request that their aircraft not be shown, typically for privacy reasons or operational security. Celebrities sometimes do this, and combat aircraft are not seen. Using PlaneFinder, one can often see US transport, tanker, and sometimes trainer and flight test aircraft. You never see bombers, attack aircraft, fighters, or those otherwise engaged in sensitive operations. You can often see the same in the UK, and even sometimes fighters from the RAF if you know where to look and what to look for. I don't know specifically if the Hellenic Air Force has requested that their aircraft (if ADS-B equipped) be blocked, but it would absolutely not be surprising. The lack of the aircraft on ADS-B sites such as FR24 is unsurprising and may be an indicator of a few different things, so it's hard to draw a conclusion based simply on the lack of publicly-available tracking data.


text:
Is there a "maximum" airplane count in the visible sky at a given location?
At night, I look at the planes in the sky and count them. I can normally spot between 2-5 planes, never more.
As the visible sky is always a constant area and there are security distances and aerial ways, is it possible to use a formula/approximation to determine the maximum number of visible planes in the sky?
Assume horizon to horizon visibility.
EDIT - Note to all those who spent some time for me
I didn't imagine this question would be such broad... this was just a though I had last night in my garden.
So, I have no idea how to be more precise... I learned some things of your comments, I am now reading some articles to learn what all that means (new words, moreover in English), and I will enrich the question some further day.
Thanks to all !

This actually depends a lot on which airspace you are looking at, since separation minima vary with a number of factors (procedural/surveillance airspace, controlled/uncontrolled airspace, PSR/SSR equipment, precision of surveillance equipment, wake turbulence minima, RVSM/VSM, ... the list goes on). Try specifying the exact area, and if possible please specify how large an area you are able to visually observe. Even with these details, an answer would be purely theoretical (and probably much larger than you might think)

I think the tag [tag:separation] would be what you want since the maximum number of airplanes is primarily restricted by aircraft separation regulations.

The airspace around London is one of the busiest airspaces in the world, but there is still physically room for many, many more planes. Feel free to start counting for yourself: https://www.flightradar24.com/51.64,-0.22/8

With usually dozens of available Flight Levels (outside mountainous terrain), you can have far more than 5 planes right above you - let alone in the visible sky. There are 3 main dimensions of separation: vertical (flight levels), lateral and longitudinal. But with planes flying in different directions at different speeds, the separation limits do not practically convert to a maximum plane density.

@J.Hougaard  Oshkosh has been known to have a few airplanes, too

When pilots fly in formation, well...

To approximate the maximum amount of aircraft flying overhead (barring special flights), you have to take the volume of the sky that you can see and divide that by the minimum separation distances between aircraft.

Go to Atlanta. You'll see a lot more than 2-5 planes. :) I enjoy flying over the Atlanta airport at high altitude at night and watching the huge swirls of traffic on approach to the various runways (they usually have 3 runways doing arrivals and 2 doing departures.)

@SMSvonderTann Minimum separation can become quite small in formation, though. :) As far as how many airplanes were ever visible at once (from a near-sea-level position on the ground, rather than, say, the ISS,) I'm guessing some of the bombing runs over Japan or perhaps Germany in WWII probably win. By 1945, a single bombing run over Japan could have several hundred B-29s accompanied by hundreds more P-51s. The USA built almost 4,000 B-29s and over 15,000 P-51s (in addition to 12,700+ B-17s.) But these numbers would still be very far from a theoretical maximum.

As the visible sky is always a constant area what if you're in a valley or on the top of a mountain?

Duplicate to http://aviation.stackexchange.com/q/11748/572 possibly...

@SentryRaven my question is not intended to be seen in a controller point of view but from a single noob as me in his garden ;)

@egid The question is, as it has been tagged, too broad to get this parameter. I assume I'm in my garden, in a more-or-less flat terrain.

@Benj Okay, just thought this might help you get more info :)

@SentryRaven sure, I learned a lot of things reading the post you linked to :) Thanks


text:
Why would this A-10 Thunderbolt be flown over rural New Hampshire?
My mother took this photo on December 29th, 2004 on a hill near Groton, New Hampshire. It appears to be an A-10 Thunderbolt, but it's difficult to tell whether or not it's armed. According to her it circled three times close above the hill before going out of sight.

The hill, as well as Grafton County as a whole, are not very populated, and there are no military bases around the area for hundreds of miles. Newspapers for the area on that day show no information that I can see. Can anyone think of a reason for an A-10 to be flown over this location on this date?

Its going to be almost impossible to tell you why, 12 years ago, an A-10 circled a hill in rural USA. Anything is going to be pure speculation, which could range from government cover-up to some pilot impressing his high school friends.

@RonBeyer -- actually, I'm pretty sure I have this question licked.

@UnrecognizedFallingObject Lets see it!

@RonBeyer I figured it would be unlikely to get an exact answer, I was hoping someone could at least say if it's normal for A-10 to be deployed in the U.S. since they're usually used overseas.

@ColinPierce They aren't "deployed" here. While they are used overseas, the A-10 crews train in the united states, including long distance sorties, training missions, even practice bombing and target shooting.

@ColinPierce flight training... Including low level flying practice, which would ideally be in areas with some terrain like hills...

@KorvinStarmast Will do, sorry, I'm bad at military terminology

@KorvinStarmast -- there are intra-CONUS training deployments, of course -- but I do see where you were getting at, the existing title was slightly clickbait-y :)

(p.s. for people wondering what I'm talking about from my above comment to Korvin -- units usually go through their deployment procedures when heading to Red Flag, for instance.)

@UnrecognizedFallingObject  Correct, and the title as edited fits the reality just fine.  (and we both know that single planes don't delploy to Red Flag ... the USAF doesn't "deploy" anywhere unless it's a two ship/section, or more. :-P

@KorvinStarmast -- indeed :) (I'm sure glad we don't have any alt-right wingnuts floating around here that would have pounced on it as originally asked!)

Practice makes perfect!
Groton, NH (along with a large chunk of rural New Hampshire further off to the north) sits more or less under an area of military Special Use Airspace called the Yankee 1 and 2 Military Operating Area complex, or MOA for short:

(If you're wondering why Groton is not on the map, ask FAA/NACO -- it's about at the bend in the road WNW of Hebron, right under the southern edge of the Yankee 1 MOA.  The snippet was taken using vfrmap.org.)
These areas of airspace are used by US military tactical pilots to practice their tactical maneuvers (such as "dry" practice bomb and strafing runs, and air combat maneuvering) without getting in the way of other airspace users -- high-performance jets making sharp maneuvers don't mix well with slow little propeller planes or not-so-maneuverable airliners!
As to why the pilot was circling?  They were probably killing time, waiting for their practice partner to show up, or the MOA to free up so they could use it.  Also, the airplane in the picture looks to be unarmed -- on one side is an empty pair of Sidewinder rails, while the other side carries a pair of targeting and countermeasures pods.
So, what your mom saw was a small part of our military keeping their gun oiled and ready, so to speak -- practice makes perfect, after all, and the airspace over rural parts of the US is about the only place in this country non-busy enough to serve as a suitable practice area.

A well educated guess, +1

This seems like the likeliest answer! She's been wondering about it for 10 years and we figured it couldn't be training since it's so isolated, but I guess it would actually be the perfect place. We never realized we lived near an MOA. Thank you!

@ColinPierce You've got it exactly backwards--the military likes isolated locations for aircraft training so they don't get too many noise complaints!

Hard to say about an A-10 to be unarmed, as it is actually a giant Gatling gun with some wings and engines mounted on in.

All airspace users should differentiate between the Yankee 1 & 2 MOAs—not only the military users—as they are two distinct airspace areas. They cover different altitudes (only Yankee 2 extends to 100 AGL) and may be active ("hot") at different times.

@vsz unless the aircraft has ammo loaded, it's unarmed.  Assuming that it always takes off for a training mission with ammo during a stateside training mission (of which gunnery is only one of many tasks trained) is a large assumption.

Each 30x173mm shell weighs 1.5 lbs, and the A-10 can carry ~1100 of them. Wonder if there's a noticeable handling difference when you shed 1700 lbs of weight and/or if they load ballast/inert ammo.

@NickT -- yeah, that would have an impact on your weight & balance.  My thinking is that they load training shells instead of "live" AP/HEI for Stateside work, but I'd have to see the W&B stuff for the A-10 to be sure.

I saw several flights of A-10s while skiing in NH in the 1980's. At one point I was above the aircraft on Mt. Attitash looking down on them roar through the canyons. I didn't know the pilots directly, but I did know one of the ground controllers who guided practice runs through the valleys. I'm sure several of them were glad for the practice before going to Afghanistan. The airplane she saw probably came out of Pease AFB.


text:
Can the lift fans used on a F-35 be driven by a turboshaft engine instead of the jet engine? If yes, which one?
This is for a sci-fi story I'm writing, so the answer doesn't have to be perfect, just close as possible.
Can the lift fans on a F-35 be driven by a turboshaft instead of the jet engine If yes, which one? The jet engine that drives the lift fans in a F-35 is called Pratt & Whitney F135  engine. The engine dumps 20,000 shaft horsepower onto  shaft that spins the fans. But i need a way to do this with a turbine, not jet engine with thrust coming from the rear.
I'm assuming that it takes a certain amount of shp (shaft horsepower) to spin the lift fans at the correct rpm.  The fictional vtol is to have 4 lift fans driven by four turbine with little heat signature to avoid infrared.

Although I'd say this is off topic, the answer is yes, of course you can. Turbine engines are used in a variety of applications; you ought to look into a turboprop, which is basically what you describe in a different configuration.

worldbuilding.SE is probably a better place for this kind of semi-fictional question

Can someone explain how this is off-topic? The question is about an aircraft power system which would seem to fit here.

You could power it with a separate engine, but that would cost added weight and space. If it was beneficial, they would've done it. To get rid of the heat signature, one could mix the exhaust with ambient air and have it exit at the top the the center of your vessel. That would mask the heat from the ground quite effectively. Another option if it's science fiction is to have it being all electric with hardly any heat production at all

There is no difference between turbofan, turboprop and turboshaft engine except for what is mounted on the shaft. There are many cores that are used in all of turbofan, turboprop and turboshaft engines. So yes, they can be driven by turboshaft. In a sense, the engine that drives them qualifies as turboshaft simply because it drives them.
That said, the lift fan of F-35 is absurdly inefficient. The thing is that lift is equal to mass flow through the fan/propeller times change of speed of the air, but the power required is equal to mass flow times square of change of speed, plus drag that grows with RPM.
Now the fan is small, so it has small mass flow and so it needs to accelerate the air to great speed and to do that it also needs high rpm, both greatly increasing the power required to spin it.
F-35 can live with that, because it only spends very short time in hover and a lot of time at high speed, so it can trade efficiency at hover for low drag at speed. But anything that should work like a helicopter should better have a large rotor like a helicopter, because it takes much less power to spin it (and thus has much lower fuel consumption).

Except that I've never heard one refer to a turbo fan as a turbo shaft engine. I think it's a grey area

@ChrisV. so far every engine had either fan or shaft, so it was called turbofan in the former and turboshaft in the later case. Some cores were already used in both configurations, but the PW F135 in F-35B is unique in that it has both fan and shaft at the same time.

What is probably another distinguishing factor between a turboshaft and turbofan is that with a turboshaft the aim is horsepower alone. With a turbofan, the core engine still produced thrust even though these days it's usually less than 20-30%. You are right the F135 is unique in that respect

@ChrisV, indeed. And F135 is a low-bypass turbofan, so it probably generates around half of thrust from the core (I can't quickly find bypass ratio though).

I'd be surprised if it was more than 30% . I believe the F16 has about 10% bypass

@ChrisV, doesn't 10% bypass mean that 90% is core?

Yes, that is correct. It was one (if not the) first bypass jet engines in a fighter jet. Before that almost all of then were straight jets. Higher bypass usually results in slow engine response (idle to full thrust) which is not preferable in a fighter

@ChrisV, The main reason why fighters can't have high bypass is that higher bypass means lower exhaust velocity, which, while great for efficiency, limits the top speed. The bypass ratio did increase a bit in fighters since F-16, but it is probably still below 1, so more than 50% is core flow (bypass ratio is bypass/core, not bypass/total).

aha, learned something new